Adapted from the best-selling novel by John Green and directed by Josh Boone, the movie is about two teenagers—Hazel (Woodley) and Gus (Ansel Egort)—who fall for each other after meeting in a cancer support group. "It changed my whole life and put things in perspective," says Woodley. "I realized I was good at being outwardly positive because that's how I am by nature. But internally? I was so mean to myself. Realizing I needed to make a shift was a big moment for me."

A major part of Woodley's transformation came from changing her actual physical appearance, namely chopping off her trademark long tresses to take on the part of Hazel. She donated the strands to the organization Children with Hair Loss, which creates wigs for those in need. Together with the group, she started a Hair for Hazel campaign, urging other young women to do the same. "We got thousands of girls to do it." To this day, the #HairForHazel hashtag on Twitter yields daily photos of young women chopping off and donating their locks.

Courtesy Photo

For Woodley, her cropped 'do represents a new chapter in her life. "When I finally realized I have to live life for myself and not for anyone else is when I started being more generous and kind and grateful. I was able to give back more," she says. "Doing the right thing always makes you feel good, and it's contagious."

Not ready to cut off your own hair, but want to support the Children with Hair Loss organization? You can purchase a limited-edition #HairForHazel T-shirt on teespring.com now, with all of the proceeds going to benefit the cause. To learn more about Children with Hair Loss, visit childrenwithhairloss.us.